Several procedures have been employed to make teeth look white. They are divided into two categories.    (1) One which is intended to remove stains adhering teeth, thereby making teeth look as white as original.    (2) One which is intended to make teeth look whiter than original.
The first procedure includes physical ones such as brushing with a toothbrush and a dentifrice containing an abrasive, and chemical ones such as decomposition of stains with a solubilizer (e.g., ethylene glycol and polyvinyl pyrrolidone), enzyme, chelating agent, or the like.
The second procedure includes bleaching with a peroxide (common practice in the West), coating with a masking agent (typified by tooth manicure), and laminate veneer technique.
The recent increasing interest in dental health and aesthetic appreciation has shifted the procedure for tooth whitening from “cleaning” to “making teeth look white”. However, bleaching with a peroxide is not approved for domestic use because of its complex procedure and danger, although limited bleaching agents are commercially available for dentists. On the other hand, coating with manicure lacks natural appearance and also lacks durability (it easily peels off after eating and drinking). Laminate veneer technique belongs to the dentist's domain. Moreover, it necessitates grinding the surface of healthy teeth, and the ground teeth cannot be restored even though the patient is not satisfied with the results of operation.
For the reasons mentioned above, there has been a demand for improvement in the conventional technique of “making teeth look white”. Such improvement should meet requirements for aesthetical appreciation, simple and safe use, no chemical reactions involved, and easy restoration in case of dissatisfaction with results.
Among the conventional reversible (restorable) whitening techniques involving no chemical reactions is coating with manicure made of shellac, vinyl acetate resin, or acrylic resin, as proposed in Japanese Patent Laid-open Nos. Hei 4-82821, Hei 5-58844, Hei 9-100215, Hei 9-202718, and Hei 9-151123. However, these techniques still have room for improvement in color tone and durability.